Electric Drive Device and Electric Power Steering Device

ABSTRACT

Provided is an electric drive device in which heat-dissipating sections (15A) (15B) that transfer at least heat generated by a power supply circuit unit (17) and power conversion circuit units (16) to a motor housing (11) are formed on an end surface section (15) of the motor housing (11) on the opposite side from an output section of a rotating shaft (23) of an electric motor. In addition, a watertight lid member (35) that covers a through hole (41) through which the rotating shaft passes and the end of the rotating shaft (23) from the exterior is attached to the end surface section (15) around the through hole (41), and a waterproof breathable membrane (44) that prevents the passage of moisture while allowing the passage of air and water vapor is provided to part of the watertight lid member.

TECHNICAL FIELD

The present invention relates generally to an electric drive device and an electric power steering device, and particularly to an electric drive device and an electric power steering device in which an electronic control unit is provided.

BACKGROUND ART

In a general field of industrial machinery, a controlled object of a mechanical system is driven by an electric motor. In recent years, employment of an electric drive device of mechatronical integration type has been started, wherein the electric drive device includes both of an electric motor and an electronic control unit in a package, and wherein the electronic control unit includes semiconductor elements and others for controlling rotational speed and torque of the electric motor.

As an example of electric drive device of mechatronical integration type, an electric power steering device for an automotive vehicle includes an electric motor, and an electronic control unit (ECU) for controlling the electric motor, wherein the electronic control unit is configured to sense a direction and a torque of rotation of a steering shaft rotated by driver's operation of a steering wheel, and drive the electric motor based on these sensed values, to produce a steering assist torque to rotate the steering shaft in the direction of rotation of the steering shaft.

Japanese Patent Application Publication No. 2015-134598 (patent document 1) discloses a known conventional electric power steering device composed of an electric motor section and an electronic control section. In the electric motor section, an electric motor is housed in a motor housing, wherein the motor housing has a cylindrical part made of an aluminum alloy or the like. In the electronic control section, a board provided with electrical components is housed in an ECU housing, wherein the ECU housing is arranged at a side of the motor housing opposite to an output shaft of the electric motor in its axial direction. The board is provided with a power supply circuit part, a power conversion circuit part, and a control circuit part, wherein the power conversion circuit part includes power switching elements such as MOSFETs or IGBTs for driving and controlling the electric motor, and wherein the control circuit part is configured to control the power switching elements. Output terminals of the power switching elements and input terminals of the electric motor are connected electrically via a bus bar.

This electronic control part housed in the ECU housing is supplied with electric power from a power supply via a connector terminal assembly made of synthetic resin, and also supplied with a sensing signal indicating operating states and others from sensors and others. The connector terminal assembly serves as a cover covering an opening of the ECU housing while being connected to the electronic control part, and fixed to an outer surface of the ECU housing by fixing bolts.

Other known examples of electric drive device where an electronic control device is integrally provided include an electric brake device, and an electric hydraulic pressure control device for control of various hydraulic pressures. The following describes an electric power steering device as a representative example.

PRIOR ART DOCUMENT(S) Patent Document(s)

-   Patent Document 1: Japanese Patent Application Publication No.     2015-134598

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

The electric power steering device disclosed in patent document 1 is required to be made compact, because the electric power steering device is mounted within an engine room of an automotive vehicle. Especially, in an engine room of a modern automotive vehicle, many auxiliary devices such as exhaust gas treatment devices and safety enhancement devices are mounted in general. This demands to make each auxiliary device such as an electric power steering device as compact, and reduce the number of components of each auxiliary device as small as possible.

In an electric power steering device as disclosed in patent document 1, a heat sink member is arranged between a motor housing and an ECU housing for dissipating heat especially from a power supply circuit part and a power conversion circuit part to the outside. The provision of the heat sink member leads to enlarging the axial length of the electric power steering device. Moreover, since electrical components constituting the power supply circuit part and the power conversion circuit part generate a large quantity of heat, it is required to effectively dissipate the heat to the outside, especially when the electric power steering device is made compact. Accordingly, it is desirable to provide an electric drive device which is made as compact in the axial direction as possible and in which heat is effectively dissipated from a power supply circuit part and a power conversion circuit part to the outside.

Furthermore, an electric power steering device as disclosed in patent document 1 is configured to have a waterproof structure where O-rings are provided respectively between a connector case and a heat sink member and between the heat sink member and a motor housing member in order to prevent entrance of water from outside.

In an accommodation space for an electronic control part, its internal pressure fluctuates due to heat generation of the electronic control part and heat absorption of outside cool air. Such fluctuation of the internal pressure due to temperature fluctuation is suppressed by ensuring breathability between the inside of the motor housing and the accommodation space for the electronic control part by a through hole through which a rotating shaft extends.

However, if breathability between the inside of the motor housing and the accommodation space for the electronic control part is ensured by such a through hole, the internal pressure of the accommodation space may fall below an external pressure due to temperature fluctuation, and thereby cause a problem that water entering the motor housing through an output side of the motor housing is likely to enter the accommodation space of the electronic control part through the through hole. The entrance of water into the accommodation space of the electronic control part causes electric components of the electronic control part to become failed.

In view of the foregoing, it is desirable to solve at least one of the problems described above for this kind of electric drive device and electric power steering device. The present invention is made in order to respond to such a desire.

It is a first object of the present invention to provide an electric drive device and an electric power steering device capable of suppressing fluctuation of an internal pressure of an accommodation space for an electronic control part and suppressing entrance of water into the accommodation space.

It is a second object of the present invention to provide an electric drive device and an electric power steering device capable of suppressing fluctuation of an internal pressure of an accommodation space for an electronic control part and suppressing entrance of water into the accommodation space, and further capable of being made as compact in its axial direction as possible, and causing heat to be effectively dissipated from a power supply circuit part and a power conversion circuit part to the outside.

Means for Solving the Problem(s)

The present invention is characterized in a first feature that: a motor housing includes an end face part including a through hole, wherein the end face part is located opposite to an output part of a rotating shaft of an electric motor, and wherein the rotating shaft extends through the through hole; a watertight cover is attached to a portion of the end face part of the motor housing around the through hole, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

The present invention is characterized in a second feature that: a motor housing includes an end face part including a through hole, wherein the end face part is formed opposite to an output part of a rotating shaft of an electric motor, and wherein the rotating shaft extends through the through hole; the end face part of the motor housing includes heat dissipation sections to allow generated heat of a power supply circuit part and a power conversion circuit part to be transferred to the motor housing; a watertight cover is attached to a portion of the end face part of the motor housing around the through hole, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

Effect(s) of the Invention

According to the first feature of the present invention, the covering of the through hole by the watertight cover including the waterproof breathable member, serves to suppress an internal pressure of an accommodation space for an electronic control part from fluctuating, and further suppress water from entering the accommodation space.

According to the second feature of the present invention, the configuration that the generated heat of the power supply circuit part and the power conversion circuit part is transferred to the end face part of the motor housing makes it possible to shorten the axial size with no heat sink member provided. Moreover, since the motor housing has a sufficient thermal capacity, the heat generated in the power supply circuit part and the power conversion circuit part can be dissipated to the outside effectively. Furthermore, the covering of the through hole by the watertight cover including the waterproof breathable member, serves to suppress an internal pressure of an accommodation space for an electronic control part from fluctuating, and further suppress water from entering the accommodation space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a whole perspective view of a steering device as an example of device to which the present invention is applied.

FIG. 2 is a whole perspective view of an electric power steering device according to an embodiment of the present invention.

FIG. 3 is an exploded perspective view of the electric power steering device shown in FIG. 2.

FIG. 4 is a perspective view of a motor housing shown in FIG. 3.

FIG. 5 is a cutaway view of the motor housing shown in FIG. 4, where the motor housing is cut by a plane containing a central axis of the motor housing.

FIG. 6 is a perspective view of the motor housing shown in FIG. 4 where a power conversion circuit part is mounted to the motor housing.

FIG. 7 is a perspective view of the motor housing shown in FIG. 4 where a power supply circuit part is mounted to the motor housing.

FIG. 8 is a perspective view of the motor housing shown in FIG. 4 where a control circuit part is mounted to the motor housing.

FIG. 9 is a sectional view of the electric power steering device in assembled state, where an electronic control section and surroundings of the electric power steering device are cut by a plane containing its central axis.

FIG. 10 is a perspective view showing whole configuration of a watertight cover shown in FIG. 9.

FIG. 11 is a perspective view showing an exterior side of the watertight cover shown in FIG. 9.

MODE(S) FOR CARRYING OUT THE INVENTION

The following details an embodiment of the present invention with reference to the drawings. However, the present invention is not limited to the embodiment, but includes various modifications and applications belonging to technical conception of the present invention.

The following briefly describes configuration of a steering device as an example of device to which the present invention is applied, with reference to FIG. 1, prior to description of the embodiment of the present invention.

First, the following describes a steering device for steering front wheels of an automotive vehicle. Steering device 1 is configured as shown in FIG. 1. A steering shaft 2 is connected to a steering wheel not shown, and includes a lower end formed with a pinion not shown, wherein the pinion is in mesh with a rack not shown, wherein the rack extends in a vehicle body lateral direction. The rack includes ends linked to respective tie rods 3 for steering the front wheels leftward and rightward, and is housed by a rack housing 4. A rubber boot 5 is provided between rack housing 4 and each tie rod 3.

An electric power steering device 6 is provided for producing an assist torque while the steering wheel is being turned. Specifically, electric power steering device 6 includes a torque sensor 7, an electric motor section 8, and an electronic control section or unit (ECU) 9, wherein torque sensor 7 is structured to sense a direction of rotation of steering shaft 2, and a rotating torque applied to steering shaft 2, wherein electric motor section 8 is structured to apply a steering assist force to the rack via a gear 10 depending on a sensed value from torque sensor 7, and wherein electronic control section 9 is configured to control an electric motor arranged in electric motor section 8. Electric motor section 8 of electric power steering device 6 is connected to gear 10 by three bolts not shown at three spots of an outer peripheral part of an output shaft side of electric motor section 8. Electronic control section 9 is arranged at a side of electric motor section 8 opposite to an output shaft of electric motor section 8.

Electric power steering device 6 operates as follows. As the steering wheel is turned to rotate steering shaft 2 in one direction, torque sensor 7 then senses the direction of rotation of steering shaft 2, and the rotating torque applied to steering shaft 2. A control circuit part calculates a quantity of operation of the electric motor, based on a sensed value from torque sensor 7. Power switching elements of a power conversion circuit part are controlled to drive the electric motor based on the calculated quantity of operation, so that an output shaft of the electric motor is rotated to drive the steering shaft 2 in the same direction as the direction of operation of the steering wheel. The rotation of the output shaft of the electric motor is transferred to the rack via the pinion and gear 10, thereby steering the automotive vehicle. Further description is omitted because its configuration and operation are well known.

As described above, in an electric power steering device as disclosed in patent document 1, a heat sink member is arranged between a motor housing and an ECU housing for dissipating heat especially from a power supply circuit part and a power conversion circuit part to the outside. The provision of the heat sink member leads to enlarging the axial length of the electric power steering device. Moreover, since electrical components constituting the power supply circuit part and the power conversion circuit part generate a large quantity of heat, it is required to effectively dissipate the heat to the outside, especially when the electric power steering device is made compact. Accordingly, it is desirable to provide an electric drive device which is made as compact in the axial direction as possible and in which heat is effectively dissipated from a power supply circuit part and a power conversion circuit part to the outside.

Furthermore, if breathability between the inside of the motor housing and an accommodation space for an electronic control part is ensured by a through hole in order to suppress fluctuation of an internal pressure of the accommodation space, the internal pressure of the accommodation space may fall below an external pressure due to temperature fluctuation, and thereby cause a problem that water entering the motor housing through an output side of the motor housing is likely to enter the accommodation space of the electronic control part through the through hole. The entrance of water into the accommodation space of the electronic control part causes electric components of the electronic control part to become failed.

In view of the foregoing background, according to the present embodiment, an electric power steering device is proposed which is configured as follows. Specifically, according to the present embodiment: an end face part of a motor housing opposite to an output part of a rotating shaft of an electric motor includes a heat dissipation region; and at least generated heat of a power supply circuit part and a power conversion circuit part is transferred to the motor housing via the heat dissipation region. According to this configuration, the feature that the generated heat of the power supply circuit part and the power conversion circuit part is transferred to the end face part of the motor housing makes it possible to shorten the axial size with no heat sink member provided. Moreover, since the motor housing has a sufficient thermal capacity, the heat generated in the power supply circuit part and the power conversion circuit part can be dissipated to the outside effectively.

Furthermore, a watertight cover is attached to a portion of the end face part of the motor housing around the through hole, wherein the rotating shaft extends through the through hole, and wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function, and wherein the watertight cover includes a waterproof breathable membrane structured to suppress passing of water and allow passing of air and water vapor. According to this configuration, the covering of the through hole by the watertight cover including the waterproof breathable membrane, serves to suppress the internal pressure of the accommodation space for the electronic control part from fluctuating, and further suppress water from entering the accommodation space.

The following details specific configuration of the electric power steering device according to the embodiment of the present invention with reference to FIGS. 2 to 11. FIG. 2 shows whole configuration of the electric power steering device according to the present embodiment. FIG. 3 shows components of the electric power steering device shown in FIG. 2 in disassembled state as viewed diagonally. FIGS. 4 to 8 show states of assembling when the components are assembled in an assembling order. FIGS. 9 to 11 illustrate configuration of a watertight cover. The following description refers to these drawings as appropriate.

As shown in FIG. 2, the electric power steering device includes electric motor section 8 and electronic control section 9. Electric motor section 8 includes a motor housing 11 and an electric motor not shown. Motor housing 11 includes a cylindrical part made of an aluminum alloy or the like. The electric motor is housed in motor housing 11. Electronic control section 9 includes a metal cover 12, and an electronic control part not shown housed in metal cover 12. Metal cover 12 is made of an aluminum alloy or the like, and is arranged at a side of motor housing 11 opposite to the output shaft in the axial direction.

Motor housing 11 and metal cover 12 are fixed to each other at their facing end faces by bonding, welding, or bolting. Metal cover 12 is formed with an accommodation space inside thereof, which accommodates the electronic control part. The electronic control part includes a power supply circuit part for supplying electric power as required, and a power conversion circuit part having power switching elements such as MOSFETs or IGBTs for driving and controlling the electric motor of electric motor section 8, and a control circuit part for controlling the power switching elements. Output terminals of the power switching elements and input terminals of a coil of the electric motor are connected electrically via a bus bar.

A connector terminal assembly 13 is fixed to an end face of metal cover 12 by fixing bolts. Connector terminal assembly 13 includes a connector terminal forming part 13A for power supply, a connector terminal forming part 13B for sensors, and a connector terminal forming part 13C for sending a state of control to external devices. The electronic control part housed in metal cover 12 is supplied with electric power from a power supply via the connector terminal forming part 13A made of synthetic resin, and is supplied with sensing signals indicative of operating states from sensors and others via the connector terminal forming part 13B, and sends a present control state of the electric power steering device via the connector terminal forming part 13C.

FIG. 3 shows electric power steering device 6 in exploded perspective view. Inside of motor housing 11, a side yoke not shown is fitted, wherein the side yoke has an annular shape and is made of iron. The electric motor not shown is mounted inside of the side yoke. The electric motor includes an output part 14 structured to apply a steering assist force to the rack via the gear. Description of specific configuration of the electric motor is omitted because it is well known.

Motor housing 11 is made of an aluminum alloy, thereby serving as a heat sink member for dissipating heat to outside atmosphere, wherein the heat is generated by the power conversion circuit part and the power supply circuit part described below. The electric motor and motor housing 11 form the electric motor section.

Electronic control part EC is placed adjacent to and attached to an end face part 15 of motor housing 11 opposite to the output part 14 of the electric motor section. Electronic control part EC includes power conversion circuit part 16, power supply circuit part 17, and control circuit part 18. The end face part 15 of motor housing 11 is formed integrally with motor housing 11, but may be formed separately from motor housing 11 and bolted or welded to motor housing 11.

Power conversion circuit part 16, power supply circuit part 17, and control circuit part 18 form redundant systems, namely, a main electronic control system and an auxiliary electronic control system. Normally, both of the main and auxiliary electronic control systems are simultaneously employed to form a normal electronic control system. When one of the main and auxiliary electronic control systems is failed or abnormal, only the other electronic control system is employed to drive and control the electric motor with half of full performance. This ensures a limp-home function, although the performance of the electric motor is only half.

Accordingly, heat of the main electronic control system and the auxiliary electronic control system is transferred to motor housing 11.

However, although not adopted by the present embodiment, there is an alternative configuration that only the main electronic control system is normally employed to drive and control the electric motor, and when an abnormality or failure occurs in the main electronic control system, the control is switched from the main electronic control system to the auxiliary electronic control system so that the auxiliary electronic control system drives and controls the electric motor. Accordingly, the heat of the main electronic control system is normally transferred to motor housing 11. When the main electronic control system is failed or abnormal, operation of the main electronic control system is stopped and the auxiliary electronic control system is operated so that heat of the auxiliary electronic control system is transferred to motor housing 11.

Electronic control part EC is composed of power conversion circuit part 16, power supply circuit part 17, control circuit part 18, and connector terminal assembly 13, which are arranged in this order away from end face part 15 of motor housing 11. Control circuit part 18 is configured to generate control signals for driving the switching elements of power conversion circuit part 16, and includes a microcomputer and a peripheral circuit. Power supply circuit part 17 is configured to supply electric power to power conversion circuit part 16, and includes a capacitor, a coil, switching elements, and others. Power conversion circuit part 16 is configured to regulate electric power flowing through the coil of the electric motor, and includes switching elements and others forming three-phase upper and lower arms.

In electronic control part EC, power conversion circuit part 16 and power supply circuit part 17 generate more quantities of heat than others. The generated heat of power conversion circuit part 16 and power supply circuit part 17 is dissipated via motor housing 11 made of the aluminum alloy. In the present embodiment, a watertight cover 35 is attached to the end face part of motor housing 11 at the end part side of the rotating shaft of the electric motor, wherein watertight cover 35 includes a resilient function member 36 and a waterproof breathable membrane 44 as a waterproof breathable function member.

The resilient function member 36 of watertight cover 35 presses power conversion circuit part 16 to the heat dissipation part of the end surface of motor housing 11, and presses and holds power conversion circuit part 16 on the heat dissipation part. Waterproof breathable membrane 44 prevents passing of water and allows passing of air and water vapor, and thereby suppress the internal pressure of the accommodation space for the electronic control part from fluctuating, and further suppresses water from entering the accommodation space. This configuration is detailed below.

Connector terminal assembly 13, which is made of synthetic resin, is arranged between control circuit part 18 and metal cover 12, and is connected to a vehicle battery (power supply) and external control devices not shown. Connector terminal assembly 13 is also connected electrically to power conversion circuit part 16, power supply circuit part 17, and control circuit part 18.

Metal cover 12 functions to house and seal water-tightly the power conversion circuit part 16, power supply circuit part 17, and control circuit part 18. In the present embodiment, metal cover 12 is welded to motor housing 11. Since metal cover 12 is made of metal, metal cover 12 serves also to dissipate the heat from power conversion circuit part 16, power supply circuit part 17, etc. to the outside.

The following describes configuration of the components and a process of assembling the components with reference to FIGS. 4 to 8. FIG. 4 shows an exterior view of motor housing 11, and FIG. 5 shows its axial sectional view. As shown in FIGS. 4 and 5, motor housing 11 is cylindrically shaped and includes a lateral peripheral surface part 11A, end face part 15, and an end face part 19. The end face part 15 closes a first end of lateral peripheral surface part 11A, whereas the end face part 19 closes a second end of lateral peripheral surface part 11A. In the present embodiment, lateral peripheral surface part 11A and end face part 15 are formed integrally such that motor housing 11 has a cylindrical shape having a bottom. The end face part 19 serves as a cover for covering the second end of lateral peripheral surface part 11A after the electric motor is mounted inside the lateral peripheral surface part 11A.

As shown in FIG. 5, a stator 21 is fitted inside the lateral peripheral surface part 11A, wherein stator 21 is formed by winding the coil 20 around an iron core. A rotor 22 is rotatably mounted inside the stator 21, wherein a permanent magnet is embedded in rotor 22. A rotating shaft 23 is fixed to rotor 22. One end of rotating shaft 23 forms the output part 14, whereas the other end of rotating shaft 23 forms a rotation-sensing target part 24 serving as a target for sensing the rotational phase and speed of rotating shaft 23. Rotation-sensing target part 24 is provided with a permanent magnet, extending through a through hole 25 formed in end face part 15, and projecting to the outside. The rotational phase and speed of rotating shaft 23 is sensed by a magnet-sensing part such as a GMR element or the like not shown.

Referring back to FIG. 4, the surface of end face part 15 opposite to the output part 14 of rotating shaft 23 is formed with heat dissipation regions 15A and 15B for power conversion circuit part 16 and power supply circuit part 17, which is a characterizing feature. Four corners of end face part 15 are formed integrally with board-fixing projecting parts 26, each of which extends perpendicularly from end face part 15. Each board-fixing projecting part 26 is formed with a threaded hole inside. Board-fixing projecting parts 26 are configured to fix a board of control circuit part 18 described below. Each board-fixing projecting part 26 projecting from power conversion part heat dissipation region 15A described below is formed with a board-receiving part 27 having the same height as power supply part heat dissipation region 15B described below in the axial direction. Each board-receiving part 27 is configured to mount a glass epoxy board 31 of power supply circuit part 17 described below. The flat area forming the end face part 15 and extending in the radial direction and perpendicular to rotating shaft 23 is divided into two regions, namely, power conversion part heat dissipation region 15A and power supply part heat dissipation region 15B. Power conversion circuit part 16 is attached to power conversion part heat dissipation region 15A. Power supply circuit part 17 is attached to power supply part heat dissipation region 15B. In the present embodiment, the area of power conversion part heat dissipation region 15A is set larger than that of power supply part heat dissipation region 15B, for ensuring more space for mounting the power conversion circuit part 16, because power conversion circuit part 16 includes redundant systems as described above, and thereby requires a sufficient mounting space.

There is a step between power conversion part heat dissipation region 15A and power supply part heat dissipation region 15B such that power conversion part heat dissipation region 15A and power supply part heat dissipation region 15B have different heights in the axial direction (the direction in which rotating shaft 23 extends). Namely, power supply part heat dissipation region 15B is formed with an outward step away with respect to power conversion part heat dissipation region 15A in the axial direction of rotating shaft 23 of the electric motor. This step is set to have a height enough to prevent interference between power conversion circuit part 16 and power supply circuit part 17 when power supply circuit part 17 is assembled after power conversion circuit part 16 is assembled.

Power conversion part heat dissipation region 15A is formed with three heat dissipation projecting parts 28, wherein each heat dissipation projecting part 28 has a narrow rectangular shape. Heat dissipation projecting parts 28 are configured to mount power conversion circuit part 16 thereon, wherein power conversion circuit part 16 described below has redundant systems. Each heat dissipation projecting part 28 projects away from the electric motor in the direction of rotating shaft 23 of the electric motor.

Power supply part heat dissipation region 15B is generally flat and is configured to mount power supply circuit part 17 thereon, where power supply circuit part 17 is described below. Accordingly, each heat dissipation projecting part 28 serves as a heat dissipation part to transfer heat from power conversion circuit part 16 to end face part 15, whereas power supply part heat dissipation region 15B serves as a heat dissipation part to transfer heat from power supply circuit part 17 to end face part 15. Each heat dissipation projecting part 28 may be omitted so that power conversion part heat dissipation region 15A serves as a heat dissipation part to transfer heat from power conversion circuit part 16 to end face part 15.

At end face part 15 of motor housing 11 according to the present embodiment described above, the axial size can be made compact because there is no heat sink member. Moreover, since motor housing 11 has a sufficient thermal capacity, the heat generated in power supply circuit part 17 and power conversion circuit part 16 can be dissipated to the outside effectively.

FIG. 6 shows a state where power conversion circuit part 16 is placed on heat dissipation projecting parts 28. As shown in FIG. 6, power conversion circuit part 16 composed of redundant systems is placed on heat dissipation projecting parts 28 formed in power conversion part heat dissipation region 15A. The switching elements constituting the power conversion circuit part 16 are placed on a lead frame made of metal such as copper, allowing their generated heat to be dissipated effectively. The switching elements and lead frame are packaged by synthetic resin. Heat-conductive grease is provided between power conversion circuit part 16 and heat dissipation projecting part 28 so that heat is transferred from power conversion circuit part 16 to heat dissipation projecting part 28 effectively.

In this way, power conversion circuit part 16 is connected thermally to heat dissipation projecting part 28. This allows the generated heat of the switching elements to be transferred to heat dissipation projecting parts 28 effectively. Furthermore, as shown in FIG. 3, power conversion circuit part 16 is pressed and held on heat dissipation projecting part 28 by resilient function member 36 of watertight cover 35 attached to the end part of rotating shaft 23.

The heat transferred to heat dissipation projecting parts 28 is dissipated to power conversion part heat dissipation region 15A, and then to lateral peripheral surface part 11A of motor housing 11, and finally to the outside. As described above, power conversion circuit part 16 is prevented from interfering with power supply circuit part 17 described below, because the height of power conversion circuit part 16 is shorter than that of power supply part heat dissipation region 15B in the axial direction.

FIG. 7 shows a state where power supply circuit part 17 is placed over power conversion circuit part 16. As shown in FIG. 7, power supply part heat dissipation region 15B is covered by power supply circuit part 17. Power supply circuit part 17 includes glass epoxy board 31, and capacitors 29, coils 30 and others placed on glass epoxy board 31. Power supply circuit part 17 includes redundant systems, each of which includes a power supply circuit composed of capacitors 29 and coil 30 and arranged symmetrically with each other as shown in FIG. 7.

The surface of glass epoxy board 31 facing the power supply part heat dissipation region 15B is fixed to end face part 15 in contact with power supply part heat dissipation region 15B. As shown in FIG. 7, this fixing is implemented by bolting with a fixing bolt not shown through a threaded hole formed in each board-receiving part 27 of board-fixing projecting part 26, and also with a fixing bolt not shown through a threaded hole formed in power supply part heat dissipation region 15B.

The configuration that power supply circuit part 17 is based on glass epoxy board 31 allows the components of power supply circuit part 17 to be mounted on both sides of the power supply circuit part 17. The surface of glass epoxy board 31 facing the power supply part heat dissipation region 15B is provided with a sensing part for sensing the rotational phase and speed of rotating shaft 23 in cooperation with rotation-sensing target part 24 of rotating shaft 23, wherein the sensing part includes a GMR element and a sensing circuit not shown.

The configuration that glass epoxy board 31 is fixed to power supply part heat dissipation region 15B in contact with power supply part heat dissipation region 15B as described above, allows the generated heat of power supply circuit part 17 to be transferred to power supply part heat dissipation region 15B effectively. The heat transferred to power supply part heat dissipation region 15B is transferred and spread into lateral peripheral surface part 11A of motor housing 11, and then dissipated to the outside. In order to enhance the thermal conductivity, an adhesive agent or dissipation grease or dissipation sheet having a high thermal conductivity may be disposed between glass epoxy board 31 and power supply part heat dissipation region 15B.

FIG. 8 shows a state where control circuit part 18 is placed over the power supply circuit part 17. As shown in FIG. 8, electric motor section 8 is arranged over power supply circuit part 17. Microcomputers 32 and peripheral circuits 33 constituting the control circuit part 18 are placed on glass epoxy board 34. Control circuit part 18 includes redundant systems, each of which includes a control circuit composed of microcomputer 32 and peripheral circuits 33 and arranged symmetrically with each other as shown in FIG. 8. Microcomputers 32 and peripheral circuits 33 may be placed on the surface of glass epoxy board 34 facing the power supply circuit part 17.

As shown in FIG. 8, glass epoxy board 34 is fixed by fixing bolts not shown through the threaded holes formed in the top portions of board-fixing projecting parts 26. The space between glass epoxy board 31 of power supply circuit part 17 and glass epoxy board 34 of control circuit part 18 is used for arrangement of capacitors 29, coils 30 and others of power supply circuit part 17 shown in FIG. 7.

The following describes configuration of watertight cover 35 with reference to FIGS. 9 to 11. In FIG. 9, electronic control part EC is arranged adjacent to end face part 15 of motor housing 11, and is covered by metal cover 12, and is thereby accommodated in an accommodation space Sh formed by metal cover 12 and end face part 15.

A magnet hold part 37 is fixed to the end part of rotating shaft 23 opposite to output part 14, wherein a permanent magnet (sensor magnet) 38 is housed in and fixed to magnet hold part 37, wherein permanent magnet 38 forms rotation-sensing target part 24. The end part of rotating shaft 23, magnet hold part 37, and permanent magnet 38 project toward the electronic control part EC with respect to end face part 15 of motor housing 11. A magnetic sensor 39 such as a GMR element is fixed to the surface of glass epoxy board 31 of power supply circuit part 17 facing the motor housing 11, wherein power supply circuit part 17 is arranged in electronic control part EC. Magnetic sensor 39 has a magnet-sensing function and is configured to sense the rotational phase or the like of rotating shaft 23 based on rotation of permanent magnet 38.

Watertight cover 35 is fixed with a clearance around an outer periphery of magnet hold part 37 and permanent magnet 38. As shown in FIG. 9, watertight cover 35 is formed to have a hollow body having a bottom (i.e. a cup-shaped body), which is composed of a cylindrical hollow section wall part and a circular bottom wall part. This configuration is detailed below with reference to FIGS. 10 and 11. Watertight cover 35 is arranged to cover the outer periphery of magnet hold part 37 and permanent magnet 38, and is fixed tightly in a fixing hole 40 in a manner of press fit, adhesion, etc., wherein fixing hole 40 is formed in end face part 15.

Fixing hole 40 is formed in a portion of end face part 15 surrounding a through hole 41 to have a circular shape around through hole 41, wherein through hole 41 is formed at or near a center of end face part 15, wherein rotating shaft 23 extends through the through hole 41. Watertight cover 35 includes an outer peripheral surface 42 that forms a hollow section of watertight cover 35 and is fixed to an inner periphery of fixing hole 40 in a manner of press fit, adhesion, etc. A ball bearing 45 is provided in through hole 41 and is structured to support the rotating shaft 23 rotatably. In this way, the accommodation space Sh formed in electronic control part EC is basically separated water-tightly from the inside of motor housing 11 by end face part 15 and watertight cover 35.

In the present embodiment, watertight cover 35 is structured to cover the magnet hold part 37 and permanent magnet 38. However, in a case where magnet hold part 37 and permanent magnet 38 are not provided, it is sufficient that watertight cover 35 is structured to water-tightly cover the through hole 41 and the end part of rotating shaft 23.

As shown in FIGS. 10 and 11, outer peripheral surface 42 of watertight cover 35, which forms a hollow section wall part of watertight cover 35, is formed with resilient function member 36 that has a substantially rectangular shape extending radially outwardly. Resilient function member 36 includes three resilience-imparting parts 36A which are arranged at intervals of 90 degrees. Each resilience-imparting part 36A has a function of resiliently pressing a corresponding one of power conversion circuit parts 16 onto a corresponding one of heat dissipation projecting parts 28, wherein power conversion circuit parts 16 are arranged at intervals of 90 degrees similarly as shown in FIG. 6.

Watertight cover 35 is formed of aluminum alloy, synthetic resin, etc., to have a cup-shaped body, namely, a hollow body having a bottom, and include outer peripheral surface 42 formed with resilient function members 36. Resilient function members 36 may be formed by stamping a material such as a spring steel plate having a resilient function, or by imparting a resilient function to a rigid metal plate by provision of a spring not shown, to resiliently press the power conversion circuit part 16 onto heat dissipation projecting part 28.

Each resilience-imparting part 36A includes three resilient pieces 36P which have a comb-teeth shape or fork shape and are substantially evenly spaced so that resilient pieces 36P are arranged at substantially even intervals on power conversion circuit part 16 in the longitudinal direction of power conversion circuit part 16. This serves to make more uniform a surface pressure from power conversion circuit part 16 on heat dissipation projecting part 28, and thereby enhance the heat dissipation capability. The number of resilient pieces 36P is arbitrary and may be determined suitably.

In this way, power conversion circuit part 16 is pressed and held resiliently on heat dissipation projecting part 28 by resilient pieces 30P of resilient function member 36 of watertight cover 35 attached to a portion of end face part 15 around rotating shaft 23. This configuration allows the power conversion circuit part 16 to be made compact because no space of power conversion circuit part 16 is required for attachment of fixing bolts, and thereby serves to suppress enlargement of the electric power steering device. The further configuration that no fixing bolt is employed serves to reduce the number of components, and omit processing of bolt holes in which the fixing bolts are screwed, and fixing operation by the fixing bolts, and thereby reduce the manufacturing unit cost.

From a further viewpoint, it is required to suppress the internal pressure from fluctuating due to temperature fluctuation, by ensuring breathability between electronic control part EC and the inside of motor housing 11. However, if watertight cover 35 is structured to isolate the accommodation space Sh of electronic control part EC from the inside of motor housing 11, the breathability between the accommodation space Sh of electronic control part EC and the inside of motor housing 11 is lost.

If watertight cover 35 is formed with a breathing hole for breathing between the accommodation space Sh of electronic control part EC and the inside of motor housing 11 in consideration of the foregoing, water entering the motor housing 11 is likely to enter the accommodation space Sh of electronic control part EC. The entrance of water into the accommodation space Sh of electronic control part EC causes the electric circuits to become failed.

In view of the foregoing, according to the present embodiment, watertight cover 35 includes bottom wall part 35T formed with a breathing hole 43 for breathing between the accommodation space Sh of electronic control part EC and the inside of motor housing 11, wherein breathing hole 43 is provided with a waterproof breathable membrane 44. Waterproof breathable membrane 44 has both of a waterproof function and a breathing function, allowing passing of air and water vapor but preventing passing of water. Waterproof breathable membrane 44 may be implemented by composition of a polyurethane polymer and a film formed of polytetrafluoroethylene by drawing, for example.

In this way, the inside of motor housing 11 is connected for fluid communication to the accommodation space Sh of electronic control part EC via the through hole 41, the internal space of watertight cover 35, and waterproof breathable membrane 44. Accordingly, waterproof breathable membrane 44 provided in breathing hole 43 of watertight cover 35 serves to allow breathing between the accommodation space Sh of electronic control part EC and the inside of motor housing 11, and also prevent water, which enters the motor housing 11, from further entering the electronic control part EC.

As shown in FIG. 3, connector terminal assembly 13 is connected to power conversion circuit part 16, power supply circuit part 17, and control circuit part 18. Furthermore, as shown in FIG. 2, metal cover 12 is assembled to seal water-tightly the power conversion circuit part 16, power supply circuit part 17, and control circuit part 18. Assembling of the electric power steering device is thus completed.

As described above, according to the present embodiment, power conversion circuit part 16 is placed on the upper side of heat dissipation projecting part 28 formed in power conversion part heat dissipation region 15A. This allows the generated heat of the switching elements of power conversion circuit part 16 to be transferred to heat dissipation projecting part 28 effectively. Furthermore, the heat transferred to heat dissipation projecting part 28 is spread in power conversion part heat dissipation region 15A, and transferred to lateral peripheral surface part 11A of motor housing 11, and dissipated to the outside.

Similarly, power supply circuit part 17 is placed on the upper side of power supply part heat dissipation region 15B. The surface of glass epoxy board 31 of power supply circuit part 17 facing the power supply part heat dissipation region 15B, on which the circuit elements of power supply circuit part 17 are placed, is fixed to end face part 15 in contact with power supply part heat dissipation region 15B. This allows the generated heat of power supply circuit part 17 to be transferred to power supply part heat dissipation region 15B effectively. The heat transferred to power supply part heat dissipation region 15B is transferred to and spread in lateral peripheral surface part 11A of motor housing 11, and dissipated to the outside.

With the configuration described above, the heat generated in power supply circuit part 17 and power conversion circuit part 16 is transferred to end face part 15 of motor housing 11, allowing to omit a heat sink member, and thereby shorten the axial size. Moreover, since motor housing 11 has a sufficient thermal capacity, the heat generated in the power supply circuit part and the power conversion circuit part can be dissipated to the outside effectively.

Moreover, power conversion circuit part 16 is resiliently pressed and held on heat dissipation projecting part 28 by resilient function member 36 of watertight cover 35 attached to the portion of end face part 15 around the rotating shaft 23. This requires no region of power conversion circuit part 16 for attachment of fixing bolts, and thereby allows the power conversion circuit part 16 to be made compact, and thereby suppress enlargement of the electric power steering device. The omission of fixing bolts further serves to reduce the number of components, and omit processing of bolt holes in which the fixing bolts are screwed, and fixing operation by the fixing bolts, and thereby reduce the manufacturing unit cost.

Furthermore, the provision of waterproof breathable membrane 44 in breathing hole 43 of watertight cover 35 serves to ensure breathing between electronic control part EC and the inside of motor housing 11, and also prevent a situation where water entering the motor housing 11 enters the electronic control part EC.

As described above, the present invention is exemplified by the configuration that the through hole formed in the end face part of the motor housing is covered by the watertight cover including the waterproof breathable member. This serves to suppress the internal pressure of the accommodation space for the electronic control part from fluctuating, and further suppress water from entering the accommodation space.

Furthermore, the present invention is exemplified by the configuration that the end face part of the motor housing opposite to the output part of the rotating shaft of the electric motor includes the heat dissipation region, wherein at least generated heat of the power supply circuit part and the power conversion circuit part is transferred to the motor housing via the heat dissipation region. With this configuration, the heat generated in the power supply circuit part and the power conversion circuit part is transferred to the end face part of the motor housing, allowing to omit a heat sink member, and thereby shorten the axial size. Moreover, since the motor housing has a sufficient thermal capacity, the heat generated in the power supply circuit part and the power conversion circuit part can be dissipated to the outside effectively. Furthermore, the configuration that the through hole formed in the end face part of the motor housing for the rotating shaft is covered by the watertight cover including the waterproof breathable membrane, serves to suppress the internal pressure of the accommodation space for the electronic control part from fluctuating, and further suppress water from entering the accommodation space.

The present invention is not limited to the embodiment described above, but includes various modified embodiments. The described embodiment is detailed merely for easy understanding of the present invention, and the present invention is not limited to a form including all of the features described above, for example. Part of features of one of the embodiments may be replaced with features of another one of the embodiments. Features of one of the embodiments may be additionally provided with features of another one of the embodiments. Part of features of each of the embodiments may be additionally provided with other features or removed or replaced.

The electric drive device according to the embodiment described above may be exemplified as follows.

According to one aspect, an electric drive device includes: a motor housing structured to house an electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole, and wherein the electric motor is structured to drive a controlled object of a mechanical system; an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; and a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; wherein the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

According to another aspect, an electric power steering device includes: a motor housing structured to house an electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole, and wherein the electric motor is structured to drive a controlled object of a mechanical system; and an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; wherein the end face part of the motor housing includes a power conversion part heat dissipation region and a power supply part heat dissipation region; the power conversion circuit part is mounted to the power conversion part heat dissipation region in a manner to allow generated heat of the power conversion circuit part to be transferred to the motor housing via the power conversion part heat dissipation region; the power supply circuit part is mounted to the power supply part heat dissipation region in a manner to allow generated heat of the power supply circuit part to be transferred to the motor housing via the power supply part heat dissipation region; the electric drive device further includes a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

According to a preferable aspect, the electric drive device is configured such that: the watertight cover has a hollow shape having a bottom, and includes a hollow section wall part and a bottom wall part; the hollow section wall part of the watertight cover is press-fitted in a fixing hole; the fixing hole is formed around the through hole of the end face part of the motor housing; and the bottom wall part of the watertight cover includes the waterproof breathable member.

According to another preferable aspect, the electric drive device according to one of the foregoing aspects further includes a permanent magnet fixed to the end part of the rotating shaft and structured to constitute a part for sensing rotation of the rotating shaft, wherein the watertight cover covers the permanent magnet.

According to a further preferable aspect, the electric drive device according to one of the foregoing aspects is configured such that the end face part of the motor housing includes a step between the power supply part heat dissipation region and the power conversion part heat dissipation region such that the power supply part heat dissipation region projects away from the electric motor in an axial direction of the electric motor with respect to the power conversion part heat dissipation region.

According to a further preferable aspect, the electric drive device according to one of the foregoing aspects is configured such that the power conversion part heat dissipation region includes a heat dissipation projecting part projecting away from the electric motor in the axial direction of the electric motor.

According to a further preferable aspect, the electric drive device according to one of the foregoing aspects is configured such that the power conversion circuit part, the power supply circuit part, and the control circuit part of the electronic control part are arranged in this order away from the electric motor in the axial direction of the electric motor.

The electric power steering device according to the embodiment described above may be exemplified as follows.

According to one aspect, an electric power steering device includes: an electric motor structured to apply a steering assist force to a steering shaft, depending on an output from a torque sensor, wherein the torque sensor is structured to sense a direction of rotation of the steering shaft and a rotating torque applied to the steering shaft; a motor housing structured to house the electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole; an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; and a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; wherein the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

According to another aspect, an electric power steering device includes: an electric motor structured to apply a steering assist force to a steering shaft, depending on an output from a torque sensor, wherein the torque sensor is structured to sense a direction of rotation of the steering shaft and a rotating torque applied to the steering shaft; a motor housing structured to house the electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole; and an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; wherein the end face part of the motor housing includes a power conversion part heat dissipation region and a power supply part heat dissipation region; the power conversion circuit part is mounted to the power conversion part heat dissipation region in a manner to allow generated heat of the power conversion circuit part to be transferred to the motor housing via the power conversion part heat dissipation region; the power supply circuit part is mounted to the power supply part heat dissipation region in a manner to allow generated heat of the power supply circuit part to be transferred to the motor housing via the power supply part heat dissipation region; the electric drive device further includes a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.

According to a preferable aspect, the electric power steering device is configured such that: the watertight cover has a hollow shape having a bottom, and includes a hollow section wall part and a bottom wall part; the hollow section wall part of the watertight cover is press-fitted in a fixing hole; the fixing hole is formed around the through hole of the end face part of the motor housing; and the bottom wall part of the watertight cover includes the waterproof breathable member.

According to another preferable aspect, the electric power steering device according to one of the foregoing aspects further includes a permanent magnet fixed to the end part of the rotating shaft and structured to constitute a part for sensing rotation of the rotating shaft, wherein the watertight cover covers the permanent magnet.

According to a further preferable aspect, the electric power steering device according to one of the foregoing aspects is configured such that the end face part of the motor housing includes a step between the power supply part heat dissipation region and the power conversion part heat dissipation region such that the power supply part heat dissipation region projects away from the electric motor in an axial direction of the electric motor with respect to the power conversion part heat dissipation region.

According to a further preferable aspect, the electric power steering device according to one of the foregoing aspects is configured such that the power conversion part heat dissipation region includes a heat dissipation projecting part projecting away from the electric motor in the axial direction of the electric motor.

According to a further preferable aspect, the electric power steering device according to one of the foregoing aspects is configured such that the power conversion circuit part, the power supply circuit part, and the control circuit part of the electronic control part are arranged in this order away from the electric motor in the axial direction of the electric motor. 

1-14. (canceled)
 15. An electric drive device comprising: a motor housing structured to house an electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole, and wherein the electric motor is structured to drive a controlled object of a mechanical system; an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; and a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; wherein the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.
 16. An electric drive device comprising: a motor housing structured to house an electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole, and wherein the electric motor is structured to drive a controlled object of a mechanical system; and an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; wherein the end face part of the motor housing includes a power conversion part heat dissipation region and a power supply part heat dissipation region; the power conversion circuit part is mounted to the power conversion part heat dissipation region in a manner to allow generated heat of the power conversion circuit part to be transferred to the motor housing via the power conversion part heat dissipation region; the power supply circuit part is mounted to the power supply part heat dissipation region in a manner to allow generated heat of the power supply circuit part to be transferred to the motor housing via the power supply part heat dissipation region; the electric drive device further comprises a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.
 17. The electric drive device according to claim 16, wherein: the watertight cover has a hollow shape having a bottom, and includes a hollow section wall part and a bottom wall part; the hollow section wall part of the watertight cover is press-fitted in a fixing hole; the fixing hole is formed around the through hole of the end face part of the motor housing; and the bottom wall part of the watertight cover includes the waterproof breathable member.
 18. The electric drive device according to claim 16, further comprising a permanent magnet fixed to the end part of the rotating shaft and structured to constitute a part for sensing rotation of the rotating shaft, wherein the watertight cover covers the permanent magnet.
 19. The electric drive device according to claim 18, wherein the end face part of the motor housing includes a step between the power supply part heat dissipation region and the power conversion part heat dissipation region such that the power supply part heat dissipation region projects away from the electric motor in an axial direction of the electric motor with respect to the power conversion part heat dissipation region.
 20. The electric drive device according to claim 19, wherein the power conversion part heat dissipation region includes a heat dissipation projecting part projecting away from the electric motor in the axial direction of the electric motor.
 21. The electric drive device according to claim 20, wherein the power conversion circuit part, the power supply circuit part, and the control circuit part of the electronic control part are arranged in this order away from the electric motor in the axial direction of the electric motor.
 22. An electric power steering device comprising: an electric motor structured to apply a steering assist force to a steering shaft, depending on an output from a torque sensor, wherein the torque sensor is structured to sense a direction of rotation of the steering shaft and a rotating torque applied to the steering shaft; a motor housing structured to house the electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole; an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; and a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; wherein the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.
 23. An electric power steering device comprising: an electric motor structured to apply a steering assist force to a steering shaft, depending on an output from a torque sensor, wherein the torque sensor is structured to sense a direction of rotation of the steering shaft and a rotating torque applied to the steering shaft; a motor housing structured to house the electric motor, wherein the motor housing includes an end face part including a through hole, wherein an end part of a rotating shaft of the electric motor opposite to an output part of the rotating shaft extends through the through hole; and an electronic control part housed in an accommodation space formed by a cover attached to the end face part of the motor housing, wherein the electronic control part is placed adjacent to the end face part, and configured to drive the electric motor, wherein the electronic control part includes a control circuit part, a power supply circuit part, and a power conversion circuit part; wherein the end face part of the motor housing includes a power conversion part heat dissipation region and a power supply part heat dissipation region; the power conversion circuit part is mounted to the power conversion part heat dissipation region in a manner to allow generated heat of the power conversion circuit part to be transferred to the motor housing via the power conversion part heat dissipation region; the power supply circuit part is mounted to the power supply part heat dissipation region in a manner to allow generated heat of the power supply circuit part to be transferred to the motor housing via the power supply part heat dissipation region; the electric drive device further comprises a watertight cover attached to a portion of the end face part of the motor housing around the through hole through which the rotating shaft extends, wherein the watertight cover covers the through hole and the end part of the rotating shaft from outside and has a watertight function; and the watertight cover includes a waterproof breathable member structured to suppress passing of water and allow passing of air and water vapor.
 24. The electric power steering device according to claim 23, wherein: the watertight cover has a hollow shape having a bottom, and includes a hollow section wall part and a bottom wall part; the hollow section wall part of the watertight cover is press-fitted in a fixing hole; the fixing hole is formed around the through hole of the end face part of the motor housing; and the bottom wall part of the watertight cover includes the waterproof breathable member.
 25. The electric power steering device according to claim 24, further comprising a permanent magnet fixed to the end part of the rotating shaft and structured to constitute a part for sensing rotation of the rotating shaft, wherein the watertight cover covers the permanent magnet.
 26. The electric power steering device according to claim 24, wherein the end face part of the motor housing includes a step between the power supply part heat dissipation region and the power conversion part heat dissipation region such that the power supply part heat dissipation region projects away from the electric motor in an axial direction of the electric motor with respect to the power conversion part heat dissipation region.
 27. The electric power steering device according to claim 26, wherein the power conversion part heat dissipation region includes a heat dissipation projecting part projecting away from the electric motor in the axial direction of the electric motor.
 28. The electric power steering device according to claim 27, wherein the power conversion circuit part, the power supply circuit part, and the control circuit part of the electronic control part are arranged in this order away from the electric motor in the axial direction of the electric motor. 